Inlet swirl control for turbochargers

ABSTRACT

An inlet duct, an induction system, and a system are disclosed for directing an inlet flow into an inlet compressor for use in an internal combustion engine. An example inlet duct may include one or more relief features disposed on an inner surface of the inlet duct. The one or more relief features may be made integral with the inlet duct. The one or more relief features may be disposed to protrude into the inlet flow to cause the inlet flow to swirl before reaching the inlet compressor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/427,093 filed Apr. 21, 2009, the entire contents of whichare incorporated herein by reference for all purposes.

BACKGROUND AND SUMMARY

Turbochargers, and superchargers, may be used with internal combustionengines to increase the mass of air entering the combustion chamber ofthe engine to create more power. An inlet compressor in the form of, forexample, a radial fan pump may be disposed in an inlet duct to compressinlet air. In some cases the inlet compressor may be driven by theenergy of the exhaust gases of the engine.

Airflow characteristics at an inlet compressor inlet may affect turboinlet efficiency and reduce turbulence related noise by providingadditional margin to the compressor surge line. Specifically, thedirection of swirl relative to the compressor rotation direction canaffect both efficiency and noise. If the swirl direction is oppositefrom the compressor, turbulence and noise can result, sometimes referredto as tip-in whoosh. Inducing a swirl in the same direction as thecompressor can result in improved inlet efficiency (higher mass flowrate) and reduced noise generation.

U.S. Pat. No. 7,322,191 discloses a device for imparting a whirlingmotion on the flow of air for supplying a turbo-superchargedinternal-combustion engine. The device is designed to be interposedupstream from the elbow of an elbow-shaped duct. The duct supplies airto the supercharger. The duct has an upstream branch having a square, orrectangular, cross-section, and a downstream branch having a circularsection to facilitate formation of a helical flow through the downstreambranch. A vane is mounted oscillating about an axis in the upstreambranch. In this way, the downstream branch of the elbow portion isreached by a tangential flow that gives rise to the helical flow of theair in the downstream branch. A maximum effect in the generation of thewhirling movement is obtained when the vane is at maximum inclination.

The inventors herein have recognized issues relating to this approach.As one example, the approach causes the greatest resistance to flowthrough the duct to achieve maximum effect in the generation of thewhirling movement.

To address the above issues, a duct with highly engineered geometry,potentially via computational fluid dynamics (CFD) or physical testmethods, for directing an inlet flow into an inlet compressor of aninternal combustion engine may be provided. The inlet duct may includeone or more relief features disposed on an inner surface of the inletduct. The one or more relief features may be disposed to protrude intothe inlet flow to cause the inlet flow to swirl before reaching theinlet compressor. In one example, the one or more relief features may bemade integral with the inlet duct. Various example embodiments mayprovide the required swirl ratios with minimal added restriction, cost,manufacturing, and assembly limitations.

Various embodiments may provide elements such as relief features,internal vanes, and/or rifling to compressor inlet ducts to rotate, orswirl an inlet flow before impacting a compressor. The relief featuresmay be formed on an inside surface of the inlet duct by forming troughsin the outside surface. The elements may tune both the direction andmagnitude of rotation. The one or more of vanes, rifling, or troughs maybe added to the induction system via a variety of methods including, butnot limited to, blow molded, injection molded, cast, or hydro-formedmetal ducts. In one example, the rifling protrusions from the exteriorof the inlet ducts form a screw-shaped pattern to impart rotational flowabout the central axis of the duct, the screw-shaped pattern rotatingalong the length of the duct toward the turbocharger with a rotationaldirection that is the same as the rotational direction of thecompressor.

Various embodiments may be “tuned” during the development process. Inthis way, an optimal swirl ratio with minimal pressure drop may beachieved.

Various examples may be utilized on both gasoline, and dieselturbocharged engines. Various examples may be applied to turbocharged,and/or supercharged, engines for the purposes of inlet efficiency andnoise control. Embodiments may be used in various applicationsincluding, without limitation, automotive applications, militaryapplications, marine applications, aeronautic applications, and off-roadusage.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of a system illustrating a singlecylinder of an engine having a turbo-charging compression device, andfeatures to improve the functionality of, and/or to reduce noiseassociated with, the compression device.

FIG. 2 shows a schematic depiction of a system including an internalcombustion engine showing an example four cylinders, a turbo-chargingcompression device, and features to improve the functionality of, and/orto reduce noise associated with, the compression device.

FIG. 3A is a perspective view of an example inlet duct that may be usedto direct an inlet flow to a compressor, such as, for example, thecompressor illustrated in FIG. 1 or 2.

FIG. 3B is a cross-sectional view taken at the line 3B-3B in FIG. 3A.

FIG. 4 is a perspective view of another example inlet duct that may beused to direct an inlet flow to a compressor, such as, for example, thecompressor illustrated in FIG. 1 or 2.

FIG. 5A is a perspective view of another example inlet duct that may beused to direct an inlet flow to a compressor, such as, for example, thecompressor illustrated in FIG. 1 or 2.

FIG. 5B is an end view of the example inlet duct shown in FIG. 5A, asviewed from a direction shown with arrow 5B in FIG. 5A.

FIG. 5C is a cross-sectional view taken at the line 5C-5C in FIG. 5B.

FIGS. 3-5 are drawn to scale, although the relative dimensions may bevaried from those illustrated, if desired.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of anautomobile. Engine 10 may be controlled at least partially by a controlsystem including controller 12, and by input from a vehicle operator 132via an input device 130. In this example, input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber (i.e.,cylinder) 30 of engine 10 may include combustion chamber walls 32 withpiston 36 positioned therein. Piston 36 may be coupled to crankshaft 40so that reciprocating motion of the piston is translated into rotationalmotion of the crankshaft. Crankshaft 40 may be coupled to at least onedrive wheel of a vehicle via an intermediate transmission system.Further, a starter motor may be coupled to crankshaft 40 via a flywheelto enable a starting operation of engine 10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

In this example, intake valve 52 and exhaust valves 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.The position of intake valve 52 and exhaust valve 54 may be determinedby position sensors 55 and 57, respectively. In alternative embodiments,intake valve 52 and/or exhaust valve 54 may be controlled by electricvalve actuation. For example, cylinder 30 may alternatively include anintake valve controlled via electric valve actuation and an exhaustvalve controlled via cam actuation including CPS and/or VCT systems.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail. In someembodiments, combustion chamber 30 may alternatively or additionallyinclude a fuel injector arranged in intake passage 44 in a configurationthat provides what is known as port injection of fuel into the intakeport upstream of combustion chamber 30.

Intake passage 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion chamber 30 among other engine cylinders. The position ofthrottle plate 64 may be provided to controller 12 by throttle positionsignal TP. Intake passage 42 may include a mass air flow sensor 120 anda manifold air pressure sensor 122 for providing respective signals MAFand MAP to controller 12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof. In some embodiments, during operationof engine 10, emission control device 70 may be periodically reset byoperating at least one cylinder of the engine within a particularair/fuel ratio.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Note that various combinations of the above sensors maybe used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft. In some examples,storage medium read-only memory 106 may be programmed with computerreadable data representing instructions executable by processor 102 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 162arranged along intake manifold 44. For a turbocharger, compressor 162may be at least partially driven by a turbine 164, via, for example ashaft 166. The turbine 164 may be arranged along exhaust passage 48. Fora supercharger, compressor 162 may be at least partially driven by theengine and/or an electric machine, and may not include a turbine. Thus,the amount of compression provided to one or more cylinders of theengine via a turbocharger or supercharger may be varied by controller12.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

FIG. 2A is a schematic view illustrating an example engine configurationshowing four cylinders, and including many features similar to theexample illustrated in FIG. 1. The figures also illustrate some exampledifferences that may be possible in accordance with present disclosure.For example, FIG. 1 illustrates throttle 62 located downstream from thecompressor 162, while FIG. 2A illustrates throttle 62 located upstreamfrom the compressor 162.

Referring now to FIG. 1 and to FIG. 2A, wherein as illustrated, an inletduct 202 may be shaped to direct an inlet flow 204 into an inletcompressor 162 coupled to the internal combustion engine 10. The inletduct 202 may include one or more relief features 206 on an inner surface208 thereof. The one or more relief features 206 may be made integralwith the compressor inlet duct 202, or otherwise coupled to thecompressor inlet duct 202. The one or more relief features 206 may bedisposed to protrude into the inlet flow 204 to cause the inlet flow 204to swirl, or be given a pre-whirl, before reaching the inlet compressor162. As a result, the surge margin may be improved which may result innoise reduction. In this way, the noise from the compressor 162 may bereduced. For example, noise from a so called ‘tip-in whoosh” may bereduced. Also, or in some cases instead, mass flow into the compressormay be increased which may result in a more ideal operating point withinthe compressor map thereby improving thermodynamic efficiency.

The one or more relief features 206 may be fluid directing means. Thefluid directing means may be, for example, elongate ridges extendinginto a path, or inlet flow 204, of the induction fluid. FIGS. 2B and 2Care cross-sectional views taken at lines 2B-2B and 2C-2C respectively inFIG. 2A. FIG. 2B illustrates the elongate ridges extending into the pathof the inlet flow at a first circumferential location 215, and FIG. 2Cillustrates the elongate ridges extending into the path of the inletflow at a second circumferential location 216, downstream of the firstcircumferential location 215. In this example as the elongate ridgesextend through the inlet duct 202 from an upstream position shown inFIG. 2B, to a downstream position shown in FIG. 2C, the circumferentialposition has changed. In this example, the circumferential position ofeach of the elongate ridges has rotated in a counterclockwise directionas the elongate ridges extend longitudinally in the direction of theflow 204, where the compressor also rotates in a counterclockwisedirection.

In some examples, the inlet compressor 162 may spin in a first direction218, and the relief features may be elongate ridges that extend in aspiral fashion along the inner surface 208 of the inlet duct 202. Theelongate ridges may have a circumferential component and a longitudinalcomponent as described. The circumferential component may be in thefirst direction, e.g. in the same direction as the spin direction of theinlet compressor. The relief features may then cause the inlet flow toswirl in the first direction 220.

The relief features 206 may be formed from recesses, or troughs 210,formed on an outside surface 212 of the inlet duct 202. As stated, insome examples, the relief features 206 may be made integrally with inletduct. In some examples the inlet duct 202 may be formed using at leastone of an injection molding operation, and a blow molding operation. Inthis way costs may be contained while advantageous functionality mayalso be achieved. Also, in this way, the structural integrity of thecombination of inlet duct 202 with features in accordance with thepresent disclosure, for example features to reduce noise, may beincreased in that they may not move relative to one another. Further,the rigidity and/or stiffness of the ducts themselves may be increased,thus enabling thinner walled, lower weight, inlet ducts.

In some examples, the number of relief features 206, for example, thenumber of elongate ridges, provided may be three. The inventors hereinhave recognized that using three elongate ridges may be particularlyeffective to provide a negative swirl of particular advantage, whilestill avoiding significant pressure drop. For example, in some examples,the inventors have been able to achieve a negative pre-whirl ofapproximately 1.05% while only causing a pressure drop of approximately0.5 kpa. Thus, while in some examples more or less ridges may be used,in the particular example illustrated herein with three ridges, wherethe angle/pitch of the ridges is as shown in the figures, the unexpectedresult is achieved that substuially the desired amount of flow rotationis achieved, while minimally impacting flow resistance, as compared withtwo or four ridges, and/or ridges at other angles/pitches.

Other features, and numbered elements, illustrated in FIGS. 1 and 2,will be made apparent from the following discussion, and the otherfigures included in the present disclosure.

FIG. 3A is a perspective view illustrating another example inlet duct302 according to the current disclosure. This example illustrates one ormore, for example three, recessed features located on an outside surface312 of the inlet duct 302. The recessed features may extend into theinlet duct 302, thereby forming one or more relief features 306 locatedon the inside of the inlet duct 302. The one or more relief features 306may include three elongate ridges formed from three elongate troughs 310formed on the outside surface 312 of the inlet duct 302. The threeridges may be substantially parallel to one another, and may be arrangedat an angle 314 with a plane 316 normal to a central axis 318 of theinlet duct 302.

FIG. 3B is a cross-sectional view taken at the line 3B-3B in FIG. 3A. Asmentioned, forming the troughs 310 may be equivalent to forming therelief features 306, in this example, the ridges. The relief features306 may have a relief feature wall thickness 330, and the inlet duct 302may have an inlet duct wall thickness 332. In some examples, the relieffeature wall thickness 330 may be approximately equal to the inlet ductwall thickness 332. In other examples, the relief feature wall thickness330 may be different from the inlet duct wall thickness 332. As withsome other examples, the inlet duct 302 may be made in a singleoperation to include the relief features. Example operations mayinclude, but may not be limited to blow molding, injection molding, andthe like.

Some examples may provide an inlet duct having relief features whichprotrude into the inlet flow, but that may not include a correspondingrecess formed on the outside surface of the inlet duct. In some cases,relief features formed as such may be made integrally with the inletduct. In other cases the relief features may be added to the inlet duct,with an attachment operation.

FIG. 4 is a perspective view illustrating another example inlet duct 402according to the current disclosure. In this example, one or more relieffeatures 406 may include, for example, three ridges formingsubstantially helical protrusions 406 along an inner surface 408 of theinlet duct 402. In some examples, the one or more relief features 406may be respectively substantially equally spaced on the inner surface408. In some examples, the helical protrusions 406 may be formed byproviding troughs 410 formed into an outside surface 412 of the inletduct 402. The relief features 406 may be made integral with the inletduct 402. In some cases the inlet duct 402 may be made in a singleoperation. The relief features 406 may be made integrally with the inletduct 402 using various operations, including, but not limited to blowmolding, or injection molding.

The example illustrated shows the helically arranged protrusions 406 ona curved portion of the inlet duct 402. In other examples a straight, orsignificantly straight, portion of an inlet duct may include helicallyarranged protrusions. In either case the protrusions may, or may not,include corresponding recesses formed in the outside surface of theinlet duct.

In some examples, the one or more relief features may form a riflingpattern. The rifling pattern may include, various numbers of protrusionsextending into the inlet flow.

FIG. 5A is a perspective view illustrating another example embodiment inaccordance with the current disclosure showing a portion of an intakeduct 502, and FIG. 5B is an end view of the inlet duct 502 shown in FIG.5A, as viewed from a direction shown with arrow 5B in FIG. 5A. The inletduct 502 illustrated may include guide vanes 556 extending from aninside surface 508 of the inlet duct 502. The guide vanes 556 mayprotrude only partway inward, for example toward a central axis 518 ofthe inlet duct 502, to leave an unobstructed central area 560 in theinlet duct 502. The unobstructed central area 560 may be located betweenopposite blade tips 566 of the guide vanes 556.

In some examples, the number of guide vanes 556 may be four. The guidevanes 556 may be substantially equally spaced within the inlet duct 502.

As described earlier, the inlet compressor may spin in a firstdirection. In some examples, the guide vanes 556 may be arranged in theinlet duct 502 to have a circumferential component and a longitudinalcomponent. The circumferential component may also be in the firstdirection. The guide vanes may cause the inlet flow to swirl, also, inthe first direction.

In some examples, the guide vanes 556 may each extend toward the centralaxis 518 of the inlet duct 502 a predetermined amount 562 relative to adiameter 564 of the inlet duct 502. The inventors herein have recognizedthat by providing an unobstructed central area 560 having a particularpredetermined size relative to a total cross-sectional area of the inletduct 502 may be particularly effective to provide a negative pre-whirlof particular advantage, while still avoiding significant pressure drop.For example, in some embodiments, the inventors have been able toachieve a negative pre-whirl of 52.3% while only causing a 1.6 kpapressure drop. In some examples, the distance between the opposite bladetips 566 may be approximately equal to between one half and threefourths of the diameter 564 of the inlet duct 502. Included among suchexamples, the distance between opposite blade tips 566 may beapproximately equal to two thirds of the diameter 564 of the inlet duct502. In other words, in some cases, the guide vanes 556 may each extendtoward the central axis 518 a distance 562 of approximately one sixth ofthe diameter 564 of the inlet duct 502.

The guide vanes 556 may be included in an inlet duct that may alsoinclude fluid directing means that may be the same, or similar to, therelief features described herein. The guide vanes 556, and the relieffeatures, may be shaped and positioned to work cooperatively toadvantageous effect, such as to provide improved pre-swirl, and/orreduced pressure drop. In some examples, the guide vanes 556 may belocated upstream from the one or more relief features. In otherexamples, the guide vanes 556 may be located downstream from the one ormore relief features.

In some examples, the guide vanes 556 may be used in an inlet ductwithout the fluid directing, or relief features such as thoseillustrated herein. Further, in some cases, the relief featuresdiscussed herein may be included in an inlet duct without guide vanessuch as those illustrated herein.

In some cases, the fluid directing, or relief, features may beconfigured similar to the guide vanes 556 illustrated herein. The guidevanes 556 may be formed integrally with the inlet duct 502. In addition,the guide vanes 556, when included with relief features, may both beformed integrally with the inlet duct 502. Integral formation, ofvarious combinations of the elements described herein may, in somecases, be achieved using a blow molding operation, an injection moldingoperation, a casting operation, a hydro-forming operation, or the like.

FIG. 5C, illustrates a cross-sectional view taken at the line 5C-5C inFIG. 5B. One or more of the guide vanes 556 may be formed on an insidesurface 508 of the inlet duct 502 by forming troughs 510 on an outsidesurface 512 of the inlet duct 502. Each guide vane 556 may have opposingwalls 528 on either side of the guide vane trough 510. A trough bottom534 may close the trough 510. One or both of the opposing walls 528 mayhave a trough wall thickness 530, and the inlet duct may have a ductwall thickness 532. In some cases, the trough wall thickness 532 may beapproximately equal to the duct wall thickness 530. In other cases, thetrough wall thickness 530, and the duct wall thickness 532, may bedifferent.

In some cases, one or more of the example inlet ducts disclosed hereinmay be all or part of a primary compressor inlet duct. In some examples,one or more of the example inlet ducts may be used as all of, or partof, or with a primary turbo runner. In addition, or instead, one or moreof the example inlet ducts may be used as all of, or part of, asecondary turbo runner.

Returning again to FIGS. 1 and 2, various example embodiments areillustrated that may include an induction system 100 for use in aninternal combustion engine 10. The induction system 100 may provide aninlet compressor 162 configured to compress an induction fluid, and topass the induction fluid to a combustion chamber 30. An inlet duct 202may be provided for directing the induction fluid toward the inletcompressor 162. Relief features 206 may be formed as part of the inletduct 202. The relief features 206 may be sized and shaped to cause theinduction fluid to swirl before reaching the inlet compressor 162.

Also illustrated is an example system 200 for directing an inlet flowtoward an inlet compressor 162 for use in an internal combustion engine10. The system 200 may include three elongate protrusions 206 integrallyformed in relief on an inside surface 208 of an inlet duct 202 by threecorresponding troughs 210 formed on an outside surface 212 of the inletduct 202. The protrusions 206 may extend into the inlet duct 202 tocause the inlet flow 204 to swirl. The number of geometric features maybe application dependent, and may be best defined by CFD analysis inconjunction with dynamometer confirmation.

Some other examples may include insertion of scrolls, springs, or aseparate vane assembly into an inlet duct.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

The invention claimed is:
 1. An inlet duct for directing an inlet flowinto an inlet compressor coupled in an internal combustion engine, theinlet duct comprising: one or more relief features disposed on an innersurface of the inlet duct, the one or more relief features protrudinginto the inlet flow to cause the inlet flow to swirl before reaching theinlet compressor; and guide vanes extending from the inner surface ofthe inlet duct, wherein the guide vanes protrude only partway toward acentral axis of the inlet duct to leave an unobstructed central area inthe inlet duct.
 2. The inlet duct of claim 1, wherein the one or morerelief features include three elongate ridges formed from threecorresponding troughs formed on an outer surface of the inlet duct. 3.The inlet duct of claim 1, wherein the one or more relief featuresinclude three ridges being substantially parallel to one another andarranged at an angle with a plane normal to the central axis of theinlet duct.
 4. The inlet duct of claim 1, wherein the one or more relieffeatures include three ridges forming substantially helical protrusionsalong the inner surface, the one or more relief features beingrespectively substantially equally spaced on the inner surface.
 5. Theinlet duct of claim 1, wherein the inlet compressor spins in a firstdirection, and wherein the guide vanes are located upstream from the oneor more relief features, the guide vanes being arranged in the inletduct to have a circumferential component and a longitudinal componentwherein the circumferential component is in the first direction, andwherein the guide vanes cause the inlet flow to swirl in the firstdirection.
 6. The inlet duct of claim 1, wherein the one or more relieffeatures form a rifling pattern, and the one or more relief features areformed integral with the inlet duct.
 7. The inlet duct of claim 1,wherein the inlet compressor spins in a first direction, and wherein theone or more relief features are elongate ridges that extend in a spiralfashion along the inner surface of the inlet duct, the elongate ridgeshaving a circumferential component and a longitudinal component whereinthe circumferential component is in the first direction, and wherein theone or more relief features cause the inlet flow to swirl in the firstdirection.
 8. The inlet duct of claim 1, wherein the inlet compressor isdriven by a turbine disposed in an exhaust passage of the engine.
 9. Aninlet duct for directing an inlet flow into an inlet compressor coupledin an internal combustion engine, comprising: three elongate ridgesdisposed on an inner surface of the inlet duct and formed from threecorresponding troughs disposed on an outer surface of the inlet duct,the three elongate ridges protruding into the inlet flow to cause theinlet flow to swirl before reaching the inlet compressor.
 10. The inletduct of claim 9, wherein the three ridges are substantially parallel toone another and arranged at an angle with a plane normal to a centralaxis of the inlet duct.
 11. The inlet duct of claim 9, wherein the threeridges form substantially helical protrusions along the inner surface,the ridges being respectively substantially equally spaced on the innersurface.
 12. The inlet duct of claim 9, further comprising guide vanesextending from the inner surface of the inlet duct, wherein the guidevanes protrude only partway toward a central axis of the inlet duct toleave an unobstructed central area in the inlet duct.
 13. The inlet ductof claim 12, wherein the inlet compressor spins in a first direction,and wherein the guide vanes are located upstream from one or more relieffeatures, the guide vanes being arranged in the inlet duct to have acircumferential component and a longitudinal component wherein thecircumferential component is in the first direction, and wherein theguide vanes cause the inlet flow to swirl in the first direction. 14.The inlet duct of claim 9, wherein the ridges form a rifling pattern.15. The inlet duct of claim 12, wherein the inlet compressor spins in afirst direction, and wherein the relief features are elongate ridgesthat extend in a spiral fashion along the inner surface of the inletduct, the elongate ridges having a circumferential component and alongitudinal component wherein the circumferential component is in thefirst direction, and wherein the relief features cause the inlet flow toswirl in the first direction.
 16. The inlet duct of claim 9, wherein theinlet compressor is driven by a turbine disposed in an exhaust passageof the engine.
 17. An inlet duct for directing an inlet flow into aninlet compressor coupled in an internal combustion engine, the inletduct comprising: one or more relief features disposed on an innersurface of the inlet duct, the one or more relief features protrudinginto the inlet flow to cause the inlet flow to swirl before reaching theinlet compressor, wherein the inlet compressor spins in a firstdirection, and wherein the relief features are elongate ridges thatextend in a spiral fashion along the inner surface of the inlet duct,the elongate ridges having a circumferential component and alongitudinal component wherein the circumferential component is in thefirst direction, and wherein the relief features cause the inlet flow toswirl in the first direction.